Zoonotic Diseases

Deadly Contact

How Animals and Humans Exchange Disease

By David Quammen

National Geographic Contributing Writer

Photograph by Lynn Johnson

In September 1994, a violent disease erupted among racehorses in a suburb of Brisbane, Australia. The place, called Hendra, was a quiet old neighborhood filled with racecourses, stables, newsstands that sell tip sheets, corner cafés with names like The Feed Bin, and racing people. The first victim was a pregnant mare named Drama Series, who started showing symptoms in an outlying pasture and was brought back to her trainer's stable for doctoring, where she only got worse. Three people worked to save her—the trainer himself, his stable foreman, and a veterinarian. Within two days Drama Series died, leaving the cause of her trouble uncertain. Had she been bitten by a snake? Had she eaten some poisonous weeds out in that scrubby, derelict meadow? Those hypotheses were eliminated two weeks later, when most of her stablemates fell ill. This wasn't snakebite or toxic fodder. It was something contagious.

The other horses suffered fever, respiratory distress, facial swelling, and clumsiness; in some, bloody froth came from the nostrils and mouth. Despite heroic efforts by the veterinarian, 12 more animals died within days. Meanwhile the trainer himself got sick; so did the stable foreman. The vet, who was following cautionary procedures but working amid the same mad circumstances, stayed healthy. After a few days in a hospital, the trainer died. His kidneys had failed and he couldn't breathe. The stable foreman, a bighearted man named Ray Unwin, who had merely gone home to endure his fever in private, survived. He and the veterinarian told me their stories when I found them in Hendra last year. Ray Unwin is a middle-aged working bloke with a sandy red ponytail and a weary sadness in his eyes, who professed that he wasn't a "whinger" (complainer) but said his health has been "crook" (not right) since it happened.

Laboratory analysis revealed that the horses and the men were infected by a previously unknown virus. At first the lab people called it equine morbillivirus, meaning a horse virus closely related to measles. Later, as its uniqueness became better appreciated, it was renamed after the place itself: Hendra. The veterinarian, a tall, gentle fellow named Peter Reid, told me that "the speed with which it went through those horses was unbelievable." At the height of the crisis, seven animals had succumbed to ugly deaths or required euthanasia within just 12 hours. One of them died thrashing and gasping so desperately that Reid couldn't get close enough to give it the merciful needle. "I'd never seen a virus do anything like that before," he said. A man of understatement, he recalled it as "a pretty traumatic time."

Identifying the new virus was only step one in solving the immediate mystery of Hendra, let alone understanding the case in a wider context. Step two involved tracking that virus to its hiding place. Where did the thing exist when it wasn't killing horses and people? Step three entailed asking a further cluster of questions: How did it emerge from its secret refuge, and why here, and why now?

After our first conversation, Peter Reid drove me out to the site where Drama Series took sick. Tract houses on prim lanes have been built over the original pasture. Not much of the old landscape remains. But toward the end of one street is a circle, called Calliope Circuit, in the middle of which stands a single mature tree, a native fig, beneath which the mare would have found shelter from eastern Australia's fierce subtropical sun.